This invention is directed to an apparatus and method for recovering liquids from a wellbore, and particularly, to an apparatus and method for recovering hydrocarbon contaminants from a subterranean water bearing formation.
In many cases hydrocarbon liquids that leak from surface or subsurface tanks eventually seep into underground water bearing formations. The relatively low density hydrocarbon liquids collect on top of the water in the subterranean formation and pose the risk of entering water wells or running streams in areas surrounding the point where the leak has occurred. The best way to reduce these risks and their associated health hazards is to remove the hydrocarbon liquids from the water formation, preferably before they spread from the entry area.
U.S. Pat. No. 4,273,650 to Solomon illustrates one arrangement for recovering low density contaminant liquids from a water saturated subterranean formation. Solomon uses two separate electrical submersible pumps suspended in a wellbore extending substantially into the water bearing formation, through the hydrocarbon contaminant zone. The wellbore is lined with a perforated casing that allows the hydrocarbon liquid and water to collect in the wellbore in position to be pumped to the surface by the two submersible pumps. One pump operates to continuously pump water from the wellbore at a flow rate sufficient to produce a cone of depression in the water bearing formation around the wellbore. The cone of depression increases the rate of contaminant flow into the wellbore by increasing the gradient to the wellbore. The collected contaminant liquid is pumped from the well by the second submersible pump at a relatively lower flow rate.
Although Solomon proposed using two submersible electrical pumps, other pump arrangements may include an electrical submersible pump for pumping water at the relatively high flow rate, and a lower flow rate pump such as a displacement-type pump for recovering the hydrocarbon liquid from the well. The submersible pump is well suited for removing water at relatively high flow rates and a displacement-type pump, such as a bladder pump or reciprocating piston pump, is suitable for recovering the hydrocarbon liquids at a lower rate of recovery.
Where a submersible electric pump was used to lift the collected hydrocarbon liquids, downhole level controls were required to operate the submersible pump only for short periods of time when a sufficient volume of hydrocarbon liquid had built up in the well. The submersible pumps were not capable of lifting fluid at a continuous, low flow rate. Although a displacement-type hydrocarbon recovery pump could be operated continuously at a low recovery rate, and thus eliminated the need for downhole level controls, the use of a displacement-type pump for the hydrocarbon in conjunction with a submersible electric pump for the water had its own disadvantages. Where the hydrocarbon recovery pump was a pneumatic operated pump, the recovery system required separate pneumatic control lines at the surface and in the well, an air compressor, and a motor for powering the compressor. Thus, these prior systems were expensive, and required excessive maintenance of surface power and control equipment.